Polymerizable compounds having norbornanelactone structure and polymers

ABSTRACT

Disclosed herein are polymerizable compounds represented by the following formula (1):                    
     wherein one of R 1  and R 2  represents an alkyl group, which has 1 to 4 carbon atoms and is other than a tert-butyl group, and the other represents a hydrogen atom or an alkyl group which has 1 to 4 carbon atoms and is other than a tert-butyl group, R 3  to R 9  each independently represent a hydrogen atom, a silyl group, a cyano group, a hydroxyl group, a halogen atom or a monovalent nonpolymerizable organic substituent group, and A represents a polymerizable group having a carbon-carbon double bond; polymers obtained by singly polymerizing the polymerizable compounds or copolymerizing them with copolymerizable compounds; and resist compositions comprising the polymers. These polymers are useful as base polymers for resist materials for an exposure light source of a short wavelength.

BACKGROUND OF THE INVENTION

a) Field of the Invention

This invention relates to polymerizable compounds having thenorbornanelactone structure and also to polymers having the samestructure and useful as materials for electronic industry such asphotoresists.

b) Description of the Related Art

Keeping in step with a demand for still further densification andintegration of semiconductor devices in recent years, there is anincreasing move toward use of an exposure light source of a shorterwavelength in a photolithographic step. Described specifically, in placeof conventionally-employed g-beam (436 nm) and i-beam (365 nm), KrFexcimer laser (248 nm) is now coming to constitute a mainstream, and afuture move to ArF excimer laser of a still shorter wavelength (193 nm)is under investigation.

As a base polymer of a resist material for use in photolithography, useof a novolak resin has been primarily recommended when g-beam or i-beamis employed as a light source while use of a hydroxystyrene-base resinhas been recommended when KrF excimer laser is employed as a lightsource, because these phenolic resins are excellent in variousproperties required as resist materials such as post-exposure alkalisolubility, dry etching resistance and substrate adherence. Phenolicresins are however not considered to be usable as resist materials whenArF excimer laser is employed as a light source, because around 193 nm,each of them exhibits an extremely strong absorption of light, saidabsorption being ascribed to the aromatic ring.

A variety of resins containing no aromatic rings in their structureswere therefore investigated as resist materials which permit use of ArFexcimer laser as a light source. For example, processes making use of aspecific acrylic-acid-base or methacrylic-acid-base resin have beenproposed.

When a resin containing no aromatic rings therein is used as a resistmaterial, on the other hand, another problem arises in that high dryetching resistance attributed to the existence of aromatic rings as inconventional phenolic resins is not available. As a method for resolvingthis problem, it has been proposed to introduce alicyclic groups, suchas adamantane skeletons, norbornane skeletons or a terpene, in anacrylic-acid-base or methacrylic-acid-base resin. Illustrative of resistmaterials available by these processes are those disclosed in JP5-265212 A1, JP 7-199467 A1, JP 8-82925 A1, etc.

The introduction of alicyclic groups into a resin leads to animprovement in dry etching resistance, but a problem arises in that,because the hydrophopicity of the resin becomes stronger, substrateadherence becomes insufficient and pattern peeling takes place duringdevelopment. Accordingly, it has also been proposed to retain substrateadherence by introducing a lactone ring, which has polarity, in amonomer to be copolymerized. Illustrative of resist materials availableby these processes are those disclosed in J. Photopolymer Science andTechnology, 9(3), 475-487, 1996, ibid., 9(3), 509-522, 1996, ibid.,10(4), 545-550, 1997, JP 9-90637 A1, etc.

In the field of photolithography where there is a move toward shorterwavelengths, development of corresponding resist materials is essential.It is, therefore, the current circumstance that seeking for basepolymers capable of simultaneously satisfying properties such astransparency at the above wavelengths, dry etching resistance andsubstrate adherence, research is under way by trial and error.

There is, accordingly, a long standing desire for the development ofbase polymers which can satisfy all of these properties.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a polymer suitablyusable as a base polymer for a resist which permits use of ArF excimerlaser as a light source, that is, a novel polymer capable of satisfyingperformance such as transparency at 193 nm, dry etching resistance andsubstrate adherence, and also a polymerizable compound required for theproduction of the polymer. Another object of the present invention is toprovide a positive resist composition of the chemical amplificationtype, which makes use of the above-described polymer.

The present inventors have proceeded with extensive research to achievethe above-described objects. As a result, it has been found that apolymer, which contains in side chains thereof specificnorbornanelactone structures represented by the below-described formula(2), has high transparency at a short wavelength such as ArF excimerlaser and excellent dry etching resistance and substrate adherence andis useful as a polymer for a resist, especially as a polymer for apositive resist. This finding has led to completion of the presentinvention.

Specifically, the present invention provides a polymerizable compoundrepresented by the following formula (1):

wherein one of R¹ and R² represents an alkyl group, which has 1 to 4carbon atoms and is other than a tert-butyl group, and the otherrepresents a hydrogen atom or an alkyl group which has 1 to 4 carbonatoms and is other than a tert-butyl group; R³ to R⁹ each independentlyrepresent a hydrogen atom, a silyl group, a cyano group, a hydroxylgroup, a halogen atom or a monovalent nonpolymerizable organicsubstituent group; and A represents a polymerizable group having acarbon-carbon double bond.

Further, the present invention also provides a polymer having, in atleast one side chain thereof, a group represented by the followingformula (2):

wherein one of R¹ and R² represents an alkyl group, which has 1 to 4carbon atoms and is other than a tert-butyl group, and the otherrepresents a hydrogen atom or an alkyl group which has 1 to 4 carbonatoms and is other than a tert-butyl group; and R³ to R⁹ eachindependently represent a hydrogen atom, a silyl group, a cyano group, ahydroxyl group, a halogen atom or a monovalent nonpolymerizable organicsubstituent group.

In addition, the present invention also provides a polymer obtained bypolymerizing or copolymerizing the polymerizable compound represented bythe formula (1).

Moreover, the present invention also provides a positive resistcomposition comprising one of the above-described polymers and an acidyielding agent which gives off an acid when exposed to light.

As the polymer according to the present invention does not contain anyaromatic ring and has a specific norbornanelactone structure, it isexcellent in substrate adherence and dry etching resistance and issuitably usable as a resist material for an exposure light source of ashorter wavelength such as ArF excimer laser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a ¹H-NMR spectrum of a compound obtained in Example 1(solvent: deuterochloroform).

FIG. 2 is a ¹³C-NMR spectrum of the compound obtained in Example 1(solvent: deuterochloroform).

FIG. 3 is a ¹H-NMR spectrum of a compound obtained in Example 2(solvent: deuterochloroform).

FIG. 4 is a ¹³C-NMR spectrum of the compound obtained in Example 2(solvent: deuterochloroform).

FIG. 5 is a ¹³C-NMR spectrum of a homopolymer obtained in Example 3(solvent: deuteroacetone).

FIG. 6 is a ¹³C-NMR spectrum of a copolymer obtained in Example 4(solvent: deuterobenzene).

FIG. 7 is a ¹³C-NMR spectrum of a copolymer obtained in Example 5(solvent: deuteroacetone).

FIG. 8 is a ¹³C-NMR spectrum of a copolymer obtained in Example 6(solvent: deuteroacetone).

FIG. 9 is an ultraviolet-visible spectrum of a resist film obtained inExample 7.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

In the formula (1), examples of the alkyl groups having 1 to 4 carbonatoms and represented by R¹ and R² can include methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl and sec-butyl. To allow each polymeraccording to the present invention to function as a positive resistpolymer, it is necessary that these alkyl groups R¹, R² do not include atert-butyl group and at least one of R¹ and R² is an alkyl group.

Among the groups represented by R³ to R⁹ in the formula (1), the halogenatom can include, as examples, fluorine, chlorine, bromine and iodineatoms, and the monovalent nonpolymerizable organic substituent group caninclude, as examples, alkyl groups, cycloalkyl groups, aralkyl groups,haloalkyl groups, alkylsilyl groups, hydroxyalkyl groups, alkyloxyalkylgroups, formyl groups, alkylcarbonyl groups, alkyloxycarbonylmethylgroups, alkyloxy groups, a carboxyl group which may be esterified, andnitrogen-containing groups. Here, illustrative of the alkyl groups areC1-C6 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, sec-butyl, and tert-butyl. Illustrative of the cycloalkylgroups are C3-C6 cycloalkyl groups such as cyclopentyl and cyclohexyl.Illustrative of the aralkyl groups are phenyl-C1-C6 alkyl groups such asbenzyl and phenethyl, diphenylmethyl and trityl. Illustrative of thehaloalkyl groups are halo-C1-C6 alkyl groups such as trifluoromethyl,trichloromethylandbromoethyl. Illustrative of the alkylsilyl groups aretri-C1-C6 alkylsilyl groups such as trimethylsilyl, triethylsilyl,tri(n-propyl)silyl, triisopropylsilyl and tert-butyl-dimethylsilyl.Illustrative of the hydroxyalkyl groups are hydroxy-C1-C6 alkyl groupssuch as hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl and2-hydroxypropyl. Illustrative of the alkyloxyalkyl groups are C1-C6alkyloxy-C1-C6alkyl groups such as methoxymethyl, methoxyethyl andethoxyethyl. Illustrative of the alkylcarbonyl groups are C1-C6alkylcarbonyl groups such as acetyl, ethylcarbonyl and n-propylcarbonyl.Illustrative of the alkyloxycarbonylmethyl groups are C1-C6alkyloxycarbonylmethyl groups such as hydroxycarbonylmethyl,methoxycarbonylmethyl, ethoxycarbonylmethyl, n-propyloxycarbonylmethyland tert-butoxycarbonylmethyl. Illustrative of the alkyloxy groups areC1-C6 alkyloxy groups such as methoxy, ethoxy, n-propyloxy,isopropyloxy, n-butoxy, isobutoxy and t-butoxy. Illustrative of thecarboxyl group which may be esterified are carboxyl, methoxycarbonyl,ethoxycarbonyl, n-propyloxycarbonyl, isopropyloxycarbonyl,n-butoxycarbonyl, isobutoxycarbonyl, tert-butoxycarbonyl,benzyloxycarbonyl, phenethyloxycarbonyl, 1-ethoxyethoxycarbonyl,3-oxocyclohexyloxycarbonyl and 2-tetrahydropyranyloxycarbonyl.Illustrative of the nitrogen-containing groups areN,N-dimethylaminomethyl, cyanomethyl and nitromethyl.

Among those containing these groups, particularly preferred in thepresent invention are those of the formula (1) in which R³ to R⁹ eachindependently represent a hydrogen atom or a lower alkyl group. Thelower alkyl group may be one having 1 to 4 carbon atoms, examples ofwhich can include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,sec-butyl and tert-butyl.

No particular limitation is imposed on the polymerizable group having acarbon-carbon double bond and represented by A, but illustrative aregroups containing an acryloyl group, a methacryloyl group, a norborneneresidual group, a vinyl ether group, a styrene group, a hydroxystyrenegroup or the like. Of these, groups containing an acryloyl group, amethacryloyl group or a norbornene residual group are particularlypreferred in the present invention.

These groups, each of which has a carbon-carbon double bond, may becoupled with the norbornanelactone skeleton via a connecting group suchas a methylene group, an ethylene group, a propylene group, acyclopentylene group, a cyclohexylene group, a phenylene group, an ethergroup, a thioether group, a carbonyl group, an ester group or an amidegroup. Among these, those coupled via an ether group or an ester groupare preferred in the present invention.

When the polymerizable compound according to the present invention isused as a feed monomer for a resist resin, one containing an acrylate,methacrylate or norbornenecarboxylate residual group as A isparticularly preferred among the compounds described above.

No particular limitation is imposed on a process for the production ofthe polymerizable compound of the present invention. As are presentativeproduction process, however, an illustrative polymerizable compound—inwhich a group having the norbornanelactone structure (a group formed byremoving A from the compound represented by the formula (1), that is,the group (2)) is coupled with the polymerizable group having acarbon-carbon double bond—can be produced by reacting a hydroxylcompound of the group (2) with the carboxylic acid chloride of thecompound, which contains a carbon-carbon double bond, in the presence ofa base. Usable examples of the base employed here can include organicbase compounds such as triethylamine and pyridine; and inorganic basecompounds such as potassium carbonate and sodium carbonate. A variety ofsolvents can be used as needed, including benzene, toluene, xylene,hexane, cyclohexane, diethyl ether, tetrahydrofuran, dioxane, diglyme,acetone, methyl ethyl ketone, methylene chloride, chloroform, methylacetate, ethyl acetate, N,N-dimethylformamide and dimethyl sulfoxide.

The reaction temperature may preferably be from −78° C. to 150° C., with−20° C. to 100° C. being particularly preferred. In general, thereaction time may range preferably from 1 to 24 hours.

Further, a polymerizable compound—in which the above-described group (2)is coupled with a polymerizable group having a carbon-carbon double bondvia an ether group—can be produced, for example, by providing as rawmaterials the hydroxy compound of the group (2) and the hydroxide of thecompound having the carbon-carbon double bond, firstly converting one ofthe hydroxyl group into an eliminative substituent such as a halogenatom or sulfonate ester group, and then reacting both of them in thepresence of a base. As an alternative process, when the group containinga carbon-carbon double bond contains another unsaturated bond or anelectrophilic group such as epoxy or carbonyl, a polymerizable compoundcan be produced by adding a hydroxy compound of the group (2) to acompound, which has the carbon-carbon double bond, in the presence of anacid or abase. Further, a vinyl ether compound can be obtained by addinga hydroxy compound of the group (2) to acetylene in the presence of abase.

The polymerizable compound according to the present invention, which hasbeen produced by a process as described above and has a carbon-carbondouble bond, can be subjected further to the Diels-Alder reaction. Forexample, a norbornene derivative can be readily obtained form a reactionwith cyclopentadiene.

The reaction product can be purified by a usual method such asdistillation, recrystallization or column chromatography.

Incidentally, the above-described hydroxy compound of the group (2)provided as a feed material is a novel substance. A process is howeverknown for the production of a hydroxy compound in which all thesubstituents of the group (2) are hydrogen atoms (for example, J. Chem.Soc., Perkin Trans. 1, 2309-2313, 1996, etc.). Feed materials for use inthe present invention can be produced by similar processes.

For example, a hydroxy compound of the group (2)—which has the formula(1) in which R¹ or R² is a methyl group and R³ to R⁹ are hydrogenatoms—can be easily obtained by oxidizingmethyl-5-norbornene-2-carboxylic acid, which is synthetically availableby the Diels-Alder reaction of methylcyclopentadiene and acrylic acid,with an oxidizing agent capable of epoxylating a carbon-carbon doublebond. Examples of the oxidizing agent capable of epoxylating acarbon-carbon double bond can include peracetic acid, m-chloroperbenzoicacid, iodosylbenzene, hydrogen peroxide, and oxygen. The reaction isconducted in a solventless manner or in a solvent such as methylenechloride, the reaction temperature may generally range from −20° C. to100° C., and the reaction time may range from 1 to 24 hours or so. Thetarget hydroxy compound can be obtained by washing out the unreactedfeed materials and uncyclized compounds (epoxylated carboxylic acids)from the reaction mixture with an aqueous alkaline solution such as anaqueous solution of sodium hydroxycarbonate.

Further, a polymerizable compound, in which R¹ or R² is an ethyl group,and a polymerizable compound, in which R¹ or R² is a butyl group, can beproduced likewise by replacing methylcyclopentadiene withethylcyclopentadiene and butylcyclopentadiene, respectively, in theabove-described production process.

The hydroxy compound of the group (2), which is obtained by theabove-described process, is in the form of an isomer mixture of theformula (1) in which an alkyl group is bonded primarily to the positionof R¹, R² or R³. When the hydroxy compound is provided for use as a feedmonomer for a resist resin, it is unnecessary to take the trouble ofisolating these monomers, and the isomer mixture can be used as is.

The polymer according to the present invention is required only tocontain the above-described group (2) in at least one of its sidechains. No particular limitation is therefore imposed on its productionprocess, and examples of the production process can includepolymerization of the polymerizable compound (1) alone, copolymerizationof the polymerizable compound (1) with another compound copolymerizablewith the polymerizable compound (1), and addition or substitution of thegroup or groups (2) to a polymer which is available from polymerizationof a polymerizable compound having a carbon-carbon double bond.Incidentally, examples of R¹ to R² in the group (2), that is, theirpreferred groups and the like are the same as in the case of the formula(1).

In the case of the polymerization of the polymerizable compound (1)alone out of the above-mentioned production processes, a suitablepolymerization process such as radical polymerization, ionpolymerization or coordination polymerization can be chosen.

In the case of radical polymerization, the polymer can be produced bydissolving the polymerizable compound (1) in a suitable solvent and thenstirring the resulting solution in the presence of an added radicalpolymerization initiator, preferably under an inert gas atmosphere suchas nitrogen. Usable examples of the solvent can include a variety ofsolvents such as benzene, toluene, xylene, hexane, cyclohexane,methanol, ethanol, propanol, diethyl ether, tetrahydrofuran, dioxane,diglyme, propylene glycol monomethyl ether acetate, acetone, methylethyl ketone, methyl acetate, ethyl acetate, N,N-dimethylformamide anddimethylsulfoxide. Usable examples of the radical polymerizationinitiator can include azo-type polymerization initators such asazoisobutyronitrile and 2,2′-azobis(methyl 2-methylpropionate); andperoxide-type polymerization initiators such as benzoyl peroxide. Thereaction temperature may generally be in a range of from 30 to 150° C.,preferably in a range of from50 to 100° C., and the reaction time isgenerally from 1 to 24 hours.

In the present invention, it is also possible to produce a copolymer bycopolymerization of the polymerizable compound (1) with another compoundcopolymerizable with the compound (1). Illustrative of the compoundcopolymerizable with the compound (1) are acrylic acid, methacrylicacid, and acrylic acid derivative monomers and methacrylic acidderivative monomers each of which is available by substituting one ormore of the hydrogen atoms of the corresponding carboxylic acid with alike number of groups, such as methyl, ethyl, n-propyl, isopropyl,tert-butyl, cyclopentyl, cyclohexyl, 2-hydroxyethyl, norbornyl,tricyclodecanyl, adamantyl, 2-methyl-2-adamantyl, tetrahydropyranyland/or tetrahydrofuranyl; norbornene, and norbornene derivative monomerseach of which is available by substituting a part or parts thereof witha like number of alkyl, alkyloxy, hydroxyl, carboxyl and/oralkyloxycarbonyl groups; vinyl ether derivative monomers such asethylvinyl ether, cyclohexylvinyl ether and hydroxyethylvinyl ether;styrene derivative monomers such as styrene, parahydroxystyrene,paramethoxystyrene and para(tert-butoxy)styrene; and maleic anhydride.These copolymerizable compounds are not limited to single use, but twoor more of them can be copolymerized with the polymerizable compound (1)to provide a multicomponent copolymer.

When the copolymer according to the present invention is used as aresist polymer, a copolymer with an acrylic acid derivative monomer,methacrylic acid derivative monomer, norbornene derivative monomer ormaleic anhydride out of the above-described compounds is particularlypreferred. The content of the polymerizable compound of this inventionin such a copolymer may preferably be in a range of from 10 to 90% interms of the molar percentage of monomer units.

The copolymer according to the present invention can be produced by aprocess similar to the above-mentioned production process of thehomopolymer. In the case of a process making use of radicalpolymerization, for example, the copolymer can be produced by dissolvingthe polymerizable compound (1) and the above-described copolymerizablecompound in a suitable solvent and then stirring the resulting solutionin the presence of an added radical polymerization initiator, preferablyunder an inert gas atmosphere such as nitrogen. As the reaction solventand the radical polymerization initiator, those similar to theabove-mentioned ones can be used.

Further, the polymer according to the present invention can also beproduced by adding or substituting the group or groups (2) to a polymerwhich is available from polymerization of a polymerizable compoundhaving a carbon-carbon double bond. In the case of a polymer with anepoxy group, carbonyl group or the like contained in at least one ofside chains thereof, for example, the polymer according to the presentinvention can be obtained by an addition reaction with the hydroxycompound of the group (2). In the case of a polymer with a hydroxylgroup, carboxyl group, carboxylate ester group of the like contained inat lest one of side chains thereof, on the other hand, the polymeraccording to the present invention can be obtained by a substitutionreaction with the hydroxy compound of the group (2).

Incidentally, the term “polymerizable compound having a carbon-carbondouble bond” means the above-described polymerizable compound having acarbon-carbon double bond.

No particular limitation is imposed on the weight average molecularweight of the polymer according to the present invention. In general,however, the weight average molecular weight may be preferably in arange of from 1,000 to 300,000, more preferably in a range of from 3,000to 100,000, because when the polymer is used as a resist resin, anunduly low molecular weight leads to insufficient strength and hence, todifficulty in forming a resist film while an excessively high molecularweight makes it difficult to form a uniform coating film by aconventional method such as spin coating. The molecular weight of thepolymer can be adjusted as desired by controlling a reaction parametersuch as reaction temperature, monomer concentration or polymerizationinitiator concentration or, when coordinate polymerization is reliedupon, catalyst concentration.

The present invention further provides a positive resist compositionwhich comprises the above-described polymer of the present invention andan acid-yielding agent added thereto, said acid-yielding agent beingcapable of giving off an acid when exposed to light.

No particular limitation is imposed on the type of the acid-yieldingagent. Usable examples can include known acid-yielding agents, forexample, onium salts such as diphenyliodonium trifluoromethanesulfonate,bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate,bis(4-tert-butylphenyl)iodonium hexafluoroantimonate,bis(4-tert-butylphenyl)iodonium tetrafuoroborate,bis(4-tert-butyl-phenyl)iodonium hexafluorophosphate,cyclohexyl-methyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,dicyclo-hexyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, andtriphenylsulfonium camphorsulfonate; halogenated organic compounds suchas 2-methyl-4,6-bis(trichloromethyl)-s-triazine,2-phenyl-4,6-bis(trichloromethyl)-s-triazine, and2-[2-(furan-2-yl)ethenyl]-4,6-bis(trichloromethyl)-s-triazine; sulfonicacid compounds such as pyrogallol tristrifluoromethaneusulfonate;organic acid imide compounds such as N-hydroxysuccinimidetrifluoromethanesulfonate and 1,8-naphthalenedicarboxylic acid imidetrifluoromethane-sulfonate; bissulfonyldiazomethane compounds; andquinone-diazide compounds. No particular limitation is imposed on theproportion of such an acid-yielding agent, but in general, theacid-yielding agent may be added preferably in a range of from 0.1 to 30wt. %, notably in a range of from 1 to 10 wt. % based on the polymer.

Usually, the resist composition according to the present invention isused in a form dissolved in a solvent. No particular limitation isimposed on the type of the solvent insofar as it is commonly known as asolvent for resists. Illustrative are ketones such as acetone, methylethyl ketone, methyl amyl ketone, cyclopentanone and cyclohexanone;alcohols such as n-propanol, isopropanol, n-butanol, isobutanol andcyclohexanol; glycols such as ethylene glycol, propylene glycol anddiethylene glycol; glycol ethers such as ethylene glycol monoethylether, ethylene glycol monobutyl ether, propylene glycol monomethylether, propylene glycol monomethyl ether acetate and diethylene glycolmonomethyl ether; cyclic ethers such as dioxane and tetrahydrofuran; andesters such as methyl acetate, ethyl acetate, propyl acetate, methylpropionate, ethyl propionate, methyl lactate and ethyl lactate.Incidentally, commonly-employed conventional additives such assurfactants, antioxidants, sensitizers, heat stabilizers and amines canbe used as needed in combination with the resist composition accordingto the present invention.

The resist composition according to the present invention, in itsunexposed form, is either insoluble or only sparingly soluble in analkaline solution for use in development. At each exposed area, however,solubility under alkaline conditions is exhibited as will be shown belowby reaction formulas, because under the influence of an acid given offfrom the acid-yielding agent, elimination of the group (2) takes placewhen R¹ is an alkyl group (reaction formula I) or decomposition of alactone ring takes place when R² is an alkyl group (reaction formulaII), and a carboxylic acid structure is formed at the eliminated ordecomposed part. Further, this elimination or decomposition progressesin series while a protonic acid occurring upon elimination ordecomposition is acting as a catalyst. The resist composition accordingto the present invention, therefore, acts as a positive photoresist ofthe so-called chemical amplification type.

wherein R represents an alkyl group, which has 1 to 4 carbon atoms andis other than a tert-butyl group, and R′ represents a group formed byeliminating a hydrogen atom from the norbornane-ring-bonded carbon atomof R.

To induce the above-described elimination or decomposition in series bythe acid, it is essential that one or more hydrogen atoms exist on thenorbornane-ring-bonded carbon atoms of the alkyl group substituted to R¹or R². A tert-butyl group is, therefore, excluded from the alkyl grouphaving 1 to 4 carbon atoms and represented by R¹ and R² in the presentinvention.

The above-described resist composition according to the presentinvention is equipped with high transparency around 193 nm and also withpolarity sufficient to provide high substrate adherence, and moreover,is considered to have high performance in dry etching resistance. As amethod for the evaluation of dry etching resistance, there is known amethod making use of an empirical formula which expresses a correlationbetween the structure of a monomer and dry etching resistance [Ohnishiparameter=N/(Nc−No) where N, Nc and No represent the total number ofatoms, the number of carbon atoms and the number of oxygen atoms, all inthe monomer, respectively; a smaller value is considered to indicatehigher dry etching resistance] (E. Electrochem. Soc., 130(1), 143-6,1983). According to this method, the Ohnishi parameter of an inventionmonomer of the formula (1), in which a group (2) in which R¹ is a methylgroup and R² to R⁹ each independently represent a hydrogen atom iscoupled with methacrylic acid via an ester linkage, is calculated tohave a value of 3.67. Lactone-ring-containing monomers disclosed in theabove-mentioned prior art, for example, mevalonic lactone methacrylate(J. Photopolymer Science and Technology, 9(3), 457-487, 1996) andγ-butyro-lacton-2-yl methacrylate (ibid., 10(4), 545-550, 1997) arecalculated to have Ohnishi parameters of 4.67 and 5.50, respectively.The polymerizable compound according to the present invention,therefore, has indicated a small value sufficient to predict excellentdry etching resistance.

The present invention will hereinafter be described more specifically bythe following Examples. It should, however, be borne in mind that thepresent invention is by no means limited to the following Examples.

EXAMPLES 1 Production of a Compound (Hereinafter Called “MNLMA”)Represented by the Following Formula (3)

Methylcyclopentadiene (8.01 g: 100 mmol) was dissolved in methyl ethylketone (10 mL), to which acrylic acid (7.93 g: 110 mmol) was addeddropwise at 0° C. over 1 hour. The thus-obtained mixture was stirred atroom temperature for 3 hours. Light components, such as the solvent andunreacted acrylic acid, were then distilled off under reduced pressurefrom the reaction mixture, whereby methyl-5-norbornene-2-carboxylic acid(14.9 g: 98 mmol) was obtained.

The thus-obtained methyl-5-norbornene-2-carboxylic acid was dissolved inmethylene chloride (100 mL), to and in which sodium acetate (2 g) wasadded and suspended. To the suspension, 37% peracetic acid (20.1 g: 98mmol) was added dropwise at 0° C. over 1 hour. The resulting mixture wasthen stirred at the same temperature for 2 hours and further, at roomtemperature for 2 hours. The solution so obtained was washedsuccessively with a 5% aqueous solution of sodium hydrogen-carbonate,water and a saturated aqueous solution of sodium chloride (hereinafterreferred to as “saturated brine”). After the water layer was removed,anhydrous magnesium sulfate powder was added to the oil layer to dry thesame. The solvent was distilled off from the thus-obtained solution,whereby γ-lactone methyl-5,6-dihydroxy-2-norbornanecarboxylate(hereinafter called “MNLOH”) (5.0 g: 30 mmol) was obtained.

MNLOH so obtained was dissolved in methylene chloride (30 mL). Aftertriethylamine (3.9 g: 39 mmol) and 4-(dimethyl-amino)pyridine (0.18 g:1.5 mmol) were added to the solution, methacryloyl chloride (3.8 g: 36mmol) was added dropwise at 0° C. for 1 hour, and the resulting mixturewas stirred further at room temperature for 12 hours. The reactionmixture was washed successively with a 5% aqueous solution of sodiumhydrogencarbonate, water and saturated brine. After the water layer wasremoved, anhydrous magnesium sulfate powder was added to the oil layerto dry the same. After the solvent was distilled off, the residue wasdistilled under reduced pressure, whereby the target compound, MNLMA(5.7 g: 24 mmol) was obtained. An elemental analysis resulted incarbon/hydrogen/oxygen=66.0/6.8/27.2 (calculated: 66.1/6.8/27.1).

¹H-NMR spectrum and ¹³C-NMR spectrum of the substance are shown in FIG.1 and FIG. 2, respectively. In FIG. 2, peaks ascribable to the carbonatoms of carbonyl groups in a lactone and an ester are observed around179 ppm and 165 ppm, respectively; peaks ascribable to olefinic carbonatoms are observed around 136 ppm and 125 ppm, respectively; and peaksascribable to two carbon atoms of a norbornane ring, said two carbonatoms being located adjacent oxygen atoms, respectively, are observedaround 79-91 ppm. It has therefore been confirmed that the targetcompound was synthesized.

It has also been ascertained from the above-mentioned NMR spectra thatthe position of the methyl group bonded to the norbornane ring in theformula (3) is at R¹, R² and R³ in the above-mentioned formula (1) andthat the percentages of these positions are as follows: R¹/R²/R³=about60/20/20. As is evident from the foregoing, the polymerizable compoundobtained in this example is a mixture of isomers different in theposition of the methyl group. As a feed monomer for a resist resin,however, the mixture can be used as is without isolation these isomers.

EXAMPLE 2 Production of a Compound (Hereinafter Called “BNLMA”)Represented by the Following Formula (4)

n-Butylcyclopentadiene (12.22 g: 100 mmol) was dissolved in methyl ethylketone (10 mL), to which acrylic acid (7.93 g: 110 mmol) was addeddropwise at 0° C. over 1 hour. The thus-obtained mixture was stirred atroom temperature for 3 hours. Light components, such as the solvent andunreacted acrylic acid, were then distilled off under reduced pressurefrom the reaction mixture, whereby n-butyl-5-norbornene-2-carboxylicacid (15.9 g: 82 mmol) was obtained.

The thus-obtained n-butyl-5-norbornene-2-carboxylic acid was dissolvedin methylene chloride (80 mL) , to and in which sodium acetate (2 g) wasadded and suspended. To the suspension, 37% peracetic acid (16.9 g: 82mmol) was added dropwise at 0° C. over 1 hour. The resulting mixture wasthen stirred at the same temperature for 2 hours and further, at roomtemperature for 12 hours. The solution so obtained was washedsuccessively with a 5% aqueous solution of sodium hydrogencarbonate,water and saturated brine. After the water layer was removed, anhydrousmagnesium sulfate powder was added to the oil layer to dry the same. Thesolvent was distilled off from the thus-obtained solution, wherebyγ-lactone n-butyl-5,6-dihydroxy-2-norbornane-carboxylate (hereinaftercalled “BNLOH”) (8.4 g: 40 mmol) was obtained.

BNLOH so obtained was dissolved in methylene chloride (40 mL). Aftertriethylamine (5.3 g: 52 mmol) and 4-(dimethyl-amino)pyridine (0. 24 g:2.mmol) were added to the solution, methacryloyl chloride (5.0 g: 48mmol) was added dropwise at 0° C. for 1 hour, and the resulting mixturewas stirred at room temperature for 12 hours. The reaction mixture waswashed successively with a 5% aqueous solution of sodiumhydrogen-carbonate, water and saturated brine. After the water layer wasremoved, anhydrous magnesium sulfate powder was added to the oil layerto dry the same. After the solvent was distilled off from the resultantsolution, the residue was purified by chromatography on a silica gelcolumn (eluent: hexane/ethyl acetate=5/1 mixed solvent), whereby thetarget compound, BNLMA (9.3 g: 33 mmol) was obtained. An elementalanalysis of the substance resulted incarbon/hydrogen/oxygen=68.8/8.1/23.1 (calculated: 69.0/8.0/23.0).

¹H-NMR spectrum and ³C-NMR spectrum of the substance are shown in FIG. 3and FIG. 4, respectively. In FIG. 4, peaks ascribable to the carbonatoms of carbonyl groups in a lactone and an ester are observed around179 ppm and 166 ppm, respectively; peaks ascribable to olefinic carbonatoms are observed around 136 ppm and 126 ppm, respectively; and peaksascribable to two carbon atoms of a norbornane ring, said two carbonatoms being located adjacent oxygen atoms, respectively, are observedaround 79-94 ppm. It has therefore been confirmed that the targetcompound was synthesized.

Incidentally, BNLMA obtained in this example is a mixture of isomerscontaining the n-butyl group at the positions of R¹, R²and R³,respectively, in the formula (1) like MNLMA obtained in Example 1. As afeed monomer for a resist resin, however, the mixture can be used as iswithout isolation of these isomers.

EXAMPLE 3 Production of a Homopolymer of the Compound Represented by theFormula (3)

MNLMA (2.36 g: 10 mmol), which had been obtained in a similar manner asin Example 1, was dissolved in N,N-dimethylformamide (40 mL), to whichazoisobutyronitrile (AIBN) (0.16 g) was added as a polymerizationinitiator. Under a nitrogen atmosphere, the resultant mixture wasstirred at 80° C. for 5 hours. The reaction mixture was then addeddropwise into a large amount of methanol under stirring, whereby thetarget polymer (1.83 g) was obtained as a white precipitate. Themolecular weight of the resultant polymer was measured by gel permeationchromatography (GPC). As a result, the weight average molecular weightwas found to be 6,300.

A ³C-NMR spectrum of the polymer is shown in FIG. 5. In the diagram,peaks ascribable to the carbon atoms of carbonyl groups in a lactone andan ester are observed around 179 ppm and 176 ppm, respectively; andpeaks ascribable to two carbon atoms of a norbornane ring, said twocarbon atoms being located adjacent oxygen atoms, respectively, areobserved around 80-92 ppm.

EXAMPLE 4 Production of a Copolymer Represented by the Formula (5)

MNLMA (2.36 g: 10 mmol), which had been obtained in a similar manner asin Example 1, and 2-methyladamantyl methacrylate (4.69 g: 20 mmol) weredissolved in 1,4-dioxane (40 mL), to which AIBN (0.65 g) was added as apolymerization initiator. Under a nitrogen atmosphere, the resultantmixture was stirred at 80° C. for 5 hours. The reaction mixture was thenadded dropwise into a large amount of methanol under stirring, wherebythe target copolymer (3.38 g) was obtained as a white precipitate. TheGPC weight average molecular weight of the resultant copolymer was foundto be 4,800.

A ¹³C-NMR spectrum of the copolymer is shown in FIG. 6. In the diagram,peaks ascribable to the carbon atoms of carbonyl groups in a lactone andan ester are observed around 178 ppm and 176 ppm, respectively; a peakascribable to a carbon atom of an adamantane ring, said carbon atombeing one with a methyl group substituted thereto, is observed around 87ppm; and partly overlapped with this peak, peaks ascribable to twocarbon atoms of a norbornane ring, said two carbon atoms being locatedadjacent oxygen atoms, respectively, are observed around 80-92 ppm.

EXAMPLE 5 Production of a Copolymer Represented by the Formula (6)

MNLMA (4.73 g: 20 mmol), which had been obtained in a similar manner asin Example 1, and t-butyl methacrylate (2.84 g: 20 mmol) were dissolvedin 1,4-dioxane (40 mL), to which AIBN (0.65 g) was added as apolymerization initiator. Under a nitrogen atmosphere, the resultantmixture was stirred at 80° C. for 5 hours. The reaction mixture was thenadded dropwise into a large amount of methanol under stirring, wherebythe target copolymer (5.33 g) was obtained as a white precipitate. TheGPC weight average molecular weight of the resultant copolymer was foundto be 15,400.

A ¹³C-NMR spectrum of the copolymer is shown in FIG. 7. In the diagram,peaks ascribable to the carbon atoms of carbonyl groups in a lactone andan ester are observed around 179 ppm and 177 ppm, respectively; peaksascribable to the carbon atoms of the methyl groups of a tert-butylgroup are observed around 28 ppm; a peak ascribable to the quaternarycarbon atom of a tert-butyl group is observed around 81 ppm; and partlyoverlapped with this peak, peaks ascribable to two carbon atoms of anorbornane ring, said two carbon atoms being located adjacent oxygenatoms, respectively, are observed around 80-92 ppm.

EXAMPLE 6 Production of a Copolymer Represented by the Formula (7)

MNLMA (2.36 g: 10 mmol), which had been obtained in a similar manner asin Example 1, tert-butyl 5-norbornene-2-carboxylate (3.89 g: 20 mmol)and maleic anhydride (1.96 g: 20 mmol) were dissolved in 1,4-dioxane (10mL), to which 2,2′-azobis(methyl 2-metylpropionate) (0.23 g) was addedas a polymerization initiator. Under a nitrogen atmosphere, theresultant mixture was stirred at 80° C. for 20 hours. The reactionmixture was then added dropwise into a large amount of a diethylether/hexane (1/4 by volume ratio) mixed solvent under stirring, wherebythe target copolymer (4.58 g) was obtained as a white precipitate. TheGPC weight average molecular weight of the resultant copolymer was foundto be 4,700.

A ¹³C-NMR spectrum of the copolymer is shown in FIG. 8. In the diagram,a peak ascribable to the carbon atom of a carbonyl group in a lactone isobserved around 179 ppm; peaks ascribable to the carbon atoms ofcarbonyl groups in an ester and acid anhydride are observed around170-178 ppm; peaks ascribable to the carbon atoms of the methyl groupsof a tert-butyl group are observed around 28 ppm; a peak ascribable tothe quaternary carbon atom of a tert-butyl group is observed around 81ppm; and partly overlapped with this peak, peaks ascribable to twocarbon atoms of the norbornane ring, said two carbon atoms being locatedadjacent oxygen atoms, respectively, are observed around 80-92 ppm.

EXAMPLE 7

The copolymer (100 parts by weight), which had been obtained in Example5, was dissolved in a mixed solvent consisting of ethyl lactate (350parts by weight) and acetone (50 parts by weight), with whichbis(4-tert-butylphenyl)-iodonium trifluoromethanesulfonate (5 parts byweight) was mixed to prepare a resist composition. The liquidformulation so prepared was applied onto a quartz substrate by spincoating. The thus-coated quartz substrate was heated for 90 seconds on ahot plate the temperature of which was controlled at 120° C., whereby aresist film of 0.8 μm in thickness was formed.

An ultraviolet-visible spectrum of the resist firm was measured. Theresist film was confirmed to have sufficient percent transmisssionaround 193 nm, a wavelength of ArF excimer laser. Theultraviolet-visible spectrum is shown in FIG. 9.

What is claimed is:
 1. A polymerizable compound represented by thefollowing formula (1):

wherein one of R¹ and R² represents an alkyl group, which has 1 to 4carbon atoms and is other than a tert-butyl group, and the otherrepresents a hydrogen atom or an alkyl group which has 1 to 4 carbonatoms and is other than a tert-butyl group; R³ to R⁹ each independentlyrepresent a hydrogen atom, a silyl group, a cyano group, a hydroxylgroup, a halogen atom or a monovalent nonpolymerizable organicsubstituent group; and A represents a polymerizable group having acarbon-carbon double bond.
 2. A polymerizable compound according toclaim 1, wherein R³ to R⁹ each independently represent a hydrogen atomor a lower alkyl group.
 3. A polymerizable compound according to claim1, wherein A is a group containing an acryloyl group, methacryloyl groupor norbornene residual group.
 4. A polymerizable compound according toclaim 1, wherein A is a group containing an acrylate, methacrylate ornorbornenecarboxylate.
 5. A polymer having, in at least one side chainthereof, a group represented by the following formula (2):

wherein one of R¹ and R² represents an alkyl group, which has 1 to 4carbon atoms and is other than a tert-butyl group, and the otherrepresents a hydrogen atom or an alkyl group which has 1 to 4 carbonatoms and is other than a tert-butyl group; and R³ to R⁹ eachindependently represent a hydrogen atom, a silyl group, a cyano group, ahydroxyl group, a halogen atom or a monovalent nonpolymerizable organicsubstituent group.
 6. A polymer which is a polymerization orcopolymerization product of a polymerizable compound as defined inclaim
 1. 7. A polymer according to claim 6, which is a copolymerizationproduct of said polymerizable compound with at least one compoundcopolymerizable with said polymerizable compound and selected from thegroup consisting of acrylic acid derivatives, methacrylic acidderivatives, norbornene derivatives and maleic anhydride.
 8. A positiveresist composition comprising a polymer as defined in claim 5 and anacid-yielding agent which gives off an acid when exposed to light.
 9. Apolymer which is a polymerization or copolymerization product of apolymerizable compound as defined in claim 2, which is acopolymerization product of said polymerizable compound with at leastone compound copolymerizable with said polymerizable compound andselected from the group consisting of acrylic acid derivatives,methacrylic acid derivatives, norbornene derivatives and maleicanhydride.
 10. A polymer which is a polymerization or copolymerizationproduct of a polymerizable compound as defined in claim 3, which is acopolymerization product of said polymerizable compound with at leastone compound copolymerizable with said polymerizable compound andselected from the group consisting of acrylic acid derivatives,methacrylic acid derivatives, norbornene derivatives and maleicanhydride.
 11. A polymer which is a polymerization or copolymerizationproduct of a polymerizable compound as defined in claim
 4. 12. A polymeraccording to claim 11, which is a copolymerization product of saidpolymerizable compound with at least one compound copolymerizable withsaid polymerizable compound and selected from the group consisting ofacrylic acid derivatives, methacrylic acid derivatives, norbornenederivatives and maleic anhydride.
 13. A polymerizable compound accordingto claim 1, wherein one of R¹ and R² is methyl, and the other representsa hydrogen atom, and R³ to R⁹ each represent a hydrogen atom, wherein Ais a group containing an acryloyl group.
 14. A polymerizable compoundaccording to claim 1, wherein one of R¹ and R² is n-butyl, and the otherrepresents a hydrogen atom, and R³ to R⁹ each represent a hydrogen atom,wherein A is a group containing an acryloyl group.